1. Field of the Invention
This invention relates generally to an apparatus and method employed with advantage in a handy type video camera apparatus and, more specifically, to a vibration compensation system for such a camera.
2. Description of Background
At present, hand held or so-called handy type video cameras having a CCD image sensor are in widespread use. The handy type video camera apparatus is small-sized and lightweight. For this very reason, however, it has a drawback that it is susceptible to hand deviation or hand wobbling during photographing. If such hand wobbling occurs, "fine wobbling" or oscillations are produced in the picture obtained on reproduction in the case of a picture photographed with, for example, zoom-up. The result of this is that the reproduced picture becomes blurred and difficult to view.
As a means for compensating such oscillations in order to render the reproduced picture easy to view, there is known a technique of compensating hand deviation by using a correction device provided in the video camera apparatus. Among the techniques for correcting hand deviation in the correction device, there is a correction means for correcting the hand deviation by picture processing and a correction means for correcting the hand deviation by optical processing. Among the correction means for correcting hand deviation by picture processing, there are a memory control system and a CCD driving control system.
The memory control system is a system in which, if hand deviation is detected, part of the picture signal obtained upon photographing an object is taken out as a picture frame, and a picture frame of the previous field and the picture frame of the current field are moved into registration with each other. The picture in the picture field portion can be enlarged for improving the range of correction, however, if this picture is enlarged, the reproduced picture is deteriorated in quality because the picture signals are enlarged to more than the resolution of the CCD image sensor. Such deterioration in picture quality becomes all the more conspicuous as the range of correction is widened. Thus, with this previously proposed system the picture quality is lowered, while the range of correction cannot be adequately widened. Nevertheless, the correction means according to this system is constructed using only ICs and, hence, is well suited for use with a small-sized inexpensive video camera apparatus.
With the above-mentioned CCD driving control system, correction is realized by varying the timing of the reading out of the picture signals obtained upon photographing an object from the CCD image sensor when hand deviation is detected. With this system, since the range of compensation is obtained by increasing the number of pixels of the CCD image sensor, it is necessary to increase the number of pixels if hand deviation correction is to be performed, even in those cases where "oscillations" appeared to be enlarged, as in the case of the object photographed with a high magnification ratio described above. If the number of pixels is increased for assuring sufficient correction of hand deviation caused by magnified "oscillations", however, the CCD image sensor and its peripheral circuit become bulky and impractical. With the correction means employing this system, a sufficient number of pixels to correct the hand deviation caused by the magnified "oscillations" is not always assured, so that an image in the reproduced picture corresponding to the hand deviation responsible for such magnified oscillations becomes discrete. The hand deviation correction according to this system can be achieved, however, without any inconvenience with the usual photographic multiplication ratio. Nevertheless, the system is also made up only of ICs and, hence, is suited for use with a small-sized inexpensive video camera apparatus.
Among correction means for correcting hand deviation by optical processing, there have been proposed a gimbal camera system and an active camera system.
The gimbal camera system is a system in which, if hand deviation is detected, the lens unit in its entirety is moved in a direction of canceling the hand deviation, thereby correcting for the hand deviation. With this system, resolution is not deteriorated, and the range of correction may be broader than the above-described electronic techniques. Since the lens unit is moved in its entirety, however, the mechanism becomes bulky and power consumption is increased. Consequently, the correction means employing this system is suited to the case in which it is desired to achieve high resolution at the cost of size and power consumption.
The active prism system is a system in which, when performing correction of hand deviation, only a part of the lens unit is moved in the direction of canceling the hand deviation. With this system, power consumption is small and the device may be easily reduced in size, while resolution is not deteriorated and the range of compensation may be broader. If the hand deviation is compensated using the above-described active prism system, there are produced no "oscillations" in the reproduced picture, so that a handy type video camera apparatus may be achieved which is small-sized and lightweight and which is capable of achieving high picture quality.
The active prism employed in the active prism system described above is produced by interconnecting two glass plates with an expandable bellows formed by a special film and by charging the interior space formed thereby with a liquid having substantially the same optical refractive index as that of the glass plates. The active prism is arranged intermediate between the objective lens provided on the front side of the video camera unit for conducting the image from an object to the video camera unit and the CCD image sensor. The active prism is part of the lens unit for conducting the image of the object to the CCD image sensor from the objective lens. The hand deviation is corrected by varying the angles of inclination, referred to herein as apex angles, of the two glass plates in respective different longitudinal and transverse directions of the video camera unit.
These above-described correction means perform correction of hand deviation based upon detecting an amount of hand deviation and among such previously proposed deviation amount detection means, there are a motion vector detection system and an angular velocity detection system.
The motion vector detection system detects the amount and the direction of the object movement by deriving the difference between the picture signal of the current field and the picture signal of the previous field, which has been stored in a semiconductor memory. This system has the drawback that mistaken operations tend to be produced during a time of low-level illumination. The oscillation amount detection means employing this system, however, is made up using only ICs and, hence, is well suited to a small-sized inexpensive video camera apparatus.
The hand deviation correction device, employed in the above-described handy type video camera apparatus, includes an oscillation amount detection unit for detecting hand deviation of a picture caused by oscillations of the video camera unit using a motion vector detection system or an angular velocity detection system, a correction signal generator for generating a correction signal based upon an output signal of the oscillation amount detection system, and a correction system for correcting hand deviation based upon a correction signal generated by the correction signal generator by a picture processing method employing, for example, a memory control system or a CCD driving control system, or by an optical processing method employing, for example, a mechanical gimbal system or an active prism system.
Meanwhile, the angle of the video camera apparatus is changed not only by hand deviation but also due to the actual, active camera work, for example, by panning, which is a technique of horizontally moving the camera during photographing, or by tilting, which is a technique of vertically moving the camera during photographing.
Active camera work includes, in general, slow camera work and quick camera work. In addition, the camera movement velocity is changed most significantly at the initial and terminal phases of the camera work, so that frequency components from 0.5 Hz to 15 Hz are produced a result of the camera work. This range of frequencies of the camera work differs from user to user.
On the other hand, the frequency components of hand deviation in the case where the user shoots a still object without performing any camera work are 5 to 15 Hz. If the user shoots from a moving object, for example, from a moving car, the main frequency components of the hand deviation are shifted to 15 to 20 Hz, that is, toward the high-frequency side. Also, the frequency range of the hand deviation is different from person to person.
With the above-described hand deviation correction device, hand deviation is corrected by servo control for canceling picture oscillations caused by hand deviation without correcting oscillations by the camera work in the frequency range of 2 to 30 Hz, in order to take into account the hand deviation produced when the user performs the above-mentioned camera work from a moving object. Thus, the reproduced picture by the video camera apparatus is easy to view since the "oscillations" due to hand deviation are not produced.
Meanwhile, in a feedback servo loop system of a servo control circuit performing the above-described servo control, a low-pass filter is provided for prohibiting natural frequency oscillations of the feedback system due to loop disturbances.
The natural frequency of the feedback loop system in the active prism system, for example, is raised in peak gain at elevated temperature conditions and hence is shifted toward the low-frequency side. Thus, the cut-off frequency of the low-pass filter is pre-set to the low-frequency side for prohibiting oscillations at elevated temperatures.
Under conditions other than high temperatures, the natural frequency of the feedback system is restored to the higher frequency, with a decrease in temperature due to lowered peak gain. The cut-off frequency of the low-pass filter, however, is pre-set to a lower frequency. Thus, a problem is presented that the high-frequency region of the feedback loop system is cut off, such that sufficient hand deviation correction cannot be achieved.
As one previously proposed system for overcoming the above problem, there is a method in which one of the plural feedback loops having different natural frequencies is selected depending upon the temperature of the video camera unit for variably setting the natural frequency of the feedback loop systems in order to correct hand deviation, despite changes in temperature of the video camera unit so that oscillations at the natural frequency will be avoided at all times.
The hand deviation correction device, designed for carrying out the above method has a drawback in that the construction becomes complex due to the provision of plural feedback loop systems. This method also has another drawback in that limitations are imposed by the feedback loop such that it becomes difficult to increase the frequency range of the hand deviation correction system.